Fluid media and materials, such as polymeric materials like thermoplastic hot melt adhesives, polymeric coatings, paints, and other thermoplastic and/or thermosetting materials, may be foamed before being dispensed. To that end, conventional dispensing systems may introduce a gas, such as nitrogen, carbon dioxide, or shop air, into solution with a pressurized fluid material. Volumes of the compressible gas are entrained in the incompressible fluid material. When the fluid material is dispensed, the entrained volumes of gas rapidly expand and are trapped within the fluid material to generate a foamed fluid material. These trapped cells comprise small bubbles of gas distributed throughout the fluid material.
One fluid material that may be dispensed in a foamed state is molten hot melt adhesive. One effect of the gas bubbles is to act as small insulators, which lengthens the open time of a foamed hot melt adhesive for product positioning. Another effect of the gas bubbles is to reduce the working viscosity of the hot melt adhesive so that the foamed hot melt adhesive is more spreadable. Because the foamed hot melt adhesive spreads easier to cover more surface area, adhesive consumption is reduced.
Foamed hot melt adhesives feature improved performance characterized by high bond strength, longer set times, stronger bonding to porous or irregular surfaces, the ability to dispense on inclined or vertical surfaces, and improved bonding to conductive materials. Foamed hot melt adhesives reduce costs by reducing adhesive consumption. The product appearance is improved by the ability to bond heat-sensitive materials, the whiteness of the adhesive, and the narrow bond line.
Sealants represent another fluid material that may be dispensed in a foamed state to create closed-cell foam seals that act as effective, long-lasting barriers against air, dust, vapor, and fluids in various applications. The sealant may be any pumpable material, such as polyurethane, silicone, or plastisol. Because a gas is used, foamed sealants retain their fundamental physical properties, such as temperature resistance and chemical resistance. The use of this “foam-in-place” technology for sealants reduces the use of expensive materials such as polyurethanes and silicones, improves compressibility and resilience, and reduces cure time. Foamed sealants can be applied by robotic devices, which is less labor intensive than manually applying die-cut gaskets. Automated foam-in-place gasketing increases production, reduces labor and material costs, and improves quality through accurate and consistent gasket placement.
Although conventional dispensing systems for foamed fluid materials are adequate for their intended purpose, it would nevertheless be desirable to provide simplified dispensing apparatus and methods for efficiently and inexpensively introducing a gas into a fluid material.